Mark Appel, the No. 1 overall pick just four years ago in the June draft, was removed from the Phillies’ 40-man roster on Monday night as the team elected to protect four pitching prospects ahead of next month’s Rule 5 draft.

The Phillies added righthanders Seranthony Dominguez, Franklyn Kilome and Jose Taveras, and lefthander Ranger Suarez. Dominguez, Kilome and Suarez are 22. Taveras is 24. There is a chance all four could begin next season in double-A Reading’s starting rotation. The Phillies also claimed 23-year-old infielder Engelb Vielma from San Francisco to bring the 40-man roster to a full 40. The Phillies cleared space on the roster by designating Appel and righthander Alberto Tirado for assignment and outrighting lefthander Elniery Garcia.

“We still believe in the kid. He’s a great kid. Where we are as a franchise, it was a tough decision,” general manager Matt Klentak said of Appel. “A lot of the tools that Mark showed as an amateur that led to him being the No. 1 overall pick are still there. He has simply struggled with performance. It’s certainly not for lack of effort on his part. We think the world of the kid and wish him well.”

The Phillies chose to not protect 22-year-old centerfielder Carlos Tocci, who batted .307 last season with a .760 OPS at double A before finishing his season at triple A. It is highly likely that he will be chosen in the Rule 5 draft.

Appel, 26, has yet to reach the majors in five seasons since Houston drafted him in 2013. His time with the Phillies, who acquired him in December 2015 as part of the trade that sent Ken Giles to the Astros, has been injury plagued. He missed two months last season with a shoulder injury and missed the second half of 2016 after undergoing elbow surgery. He had a 5.27 ERA last season in 17 triple-A starts this year. Both Appel and Tirado could be traded.

Dominguez had 75 strikeouts and 30 walks in 62 1/3 innings at high-A Clearwater. Kilome reached double A last season and combined for a 2.83 ERA in 24 starts between Clearwater and Reading. He racked up 103 strikeouts and walked 52 in 127 innings. Baseball America ranked him earlier this month at the team’s 10th-best prospect.

Taveras finished the season in triple A, where he had a 1.32 ERA in seven starts. He struck out 37 and walked 15 in 41 innings with Lehigh Valley. Suarez had a 2.27 ERA last season between single-A Lakewood and Clearwater. He struck out 128 batters and walked just 35 in 122 2/3 innings over 22 starts.

“He may have been the breakout pitcher of the year for the Phillies,” Klentak said of Suarez. “We’d always heard a lot about him and this year he took his performance to another level.”

The Giants claimed Vielma off waivers last September from Minnesota. He spent most of last season in triple A, where he batted .206 with a .233 on-base percentage in 296 at-bats. He’s a good defender and can play second base and shortstop. The Phillies have six middle infielders — Vielma, Cesar Hernandez, Freddy Galvis, J.P. Crawford, Jesmuel Valentin, and Eliezer Alvarez — on the 40-man roster.